So there is apparently a mysterious Tumblr 12.07.2299 that seems to be related to the mysterious website. Of course the website itself is questionable and anyone can make Tumblr so this can of course be nothing.

According to the Fallout Wiki, Vault 74 was cut content from Fallout New Vegas so is non-canon probably but it was attacked by Raiders with the Overseer speculated to die but perhaps he is the survivor.

There are mysterious audio logs on the tumblr as well but I don't know how to post those here or if it is possible.